[SceneKit] Add AddAnimation overload that takes a SCNAnimation (#3192)

Fixes xamarin/xamarin-macios#3166

Apple broke `addAnimation:forKey:` API by changing `CAAnimation` parameter into a
`ISCNAnimationProtocol` that was introduced in Xcode 9 (iOS 11 and company).

We can't break the existing API but we can add an extension method that
reuses the `CAAnimation` overload but takes a `SCNAnimation` and we
turn the `SCNAnimation` into a `CAAnimation` behind the scenes.

For XAMCORE_4_0 we corrected the protocol signature to take `ISCNAnimationProtocol` so there won't be a need for the extension method anymore.

src/SceneKit/SCNCompat.cs

@@ -8,6 +8,7 @@ using XamCore.ObjCRuntime;
 #if WATCH
 using AnimationType = global::XamCore.SceneKit.ISCNAnimationProtocol;
 #else
+using XamCore.CoreAnimation;
 using AnimationType = global::XamCore.CoreAnimation.CAAnimation;
 #endif
 
@@ -96,4 +97,18 @@ namespace XamCore.SceneKit {
 		}
 	}
 #endif
+
+#if !WATCH && !XAMCORE_4_0
+	[iOS (11,0)]
+	[TV (11,0)]
+	[Mac (10,13,0, PlatformArchitecture.Arch64)]
+	static public partial class SCNAnimatableExtensions {
+		static public void AddAnimation (this ISCNAnimatable self, SCNAnimation animation, string key)
+		{
+			using (var ca = CAAnimation.FromSCNAnimation (animation))
+			using (var st = key != null ? new NSString (key) : null)
+				self.AddAnimation (ca, st);
+		}
+	}
+#endif
 }

src/scenekit.cs

@@ -125,7 +125,11 @@ namespace XamCore.SceneKit {
 #endif
 		[NoWatch]
 		[Export ("addAnimation:forKey:")]
+#if !XAMCORE_4_0
 		void AddAnimation (CAAnimation animation, [NullAllowed] NSString key);
+#else
+		void AddAnimation (ISCNAnimationProtocol scnAnimation, [NullAllowed] string key);
+#endif
 
 #if XAMCORE_2_0
 #if XAMCORE_4_0
@@ -3503,7 +3507,6 @@ namespace XamCore.SceneKit {
 		[Watch (4, 0), TV (11, 0), Mac (10, 13, onlyOn64: true), iOS (11, 0)]
 		[Export ("incremental")]
 		bool Incremental { [Bind ("isIncremental")] get; set; }
-		
 	}
 
 	[Watch (3,0)]

tests/monotouch-test/SceneKit/NodeTest.cs

@@ -56,7 +56,23 @@ namespace MonoTouchFixtures.SceneKit {
 				string key = "key";
 				n.AddAnimation (a, key);
 				using (var s = new NSString (key))
-					n.AddAnimation (a, key);
+					n.AddAnimation (a, s);
+			}
+		}
+
+		[Test]
+		public void AddAnimation_Overload ()
+		{
+			TestRuntime.AssertXcodeVersion (9,0);
+
+			using (var ca = CAAnimation.CreateAnimation ())
+			using (var a = SCNAnimation.FromCAAnimation (ca))
+			using (var n = SCNNode.Create ()) {
+				n.AddAnimation (a, "key");
+				n.RemoveAllAnimations ();
+
+				n.AddAnimation (a, null);
+				n.RemoveAllAnimations ();
 			}
 		}
 	}